The embodiments described herein relate generally to gas turbine engine injection nozzles, and more specifically, to pre-mix tubes that include a fuel injector used in gas turbine engine injection nozzles.
At least some known turbine engines are used in cogeneration facilities and power plants. Such engines may have high specific work and high power-per-unit mass flow requirements. To increase the operating efficiency, at least some known turbine engines, such as gas turbine engines, may operate with increased combustion temperatures. Generally, in at least some of such known gas turbine engines, engine efficiency increases as combustion gas temperatures increase. However, operating known turbine engines with higher temperatures may also increase the generation of polluting emissions, such as oxides of nitrogen (NOX). In an attempt to reduce the generation of such emissions, at least some known turbine engines include improved combustion system designs. For example, many combustion systems may use premixing technology that includes fuel injection nozzles or micro-mixers that mix substances, such as diluents, gases, and/or air with fuel to generate a fuel mixture for combustion.
Certain known gas turbine fuel injection nozzles contain many small pre-mix tubes that receive air through a main inlet, and fuel through at least one fuel injector along the length of the tube. Each pre-mix tube is positioned between upstream and downstream plates and is surrounded by a peripheral wall that forms a fuel nozzle head. The fuel injectors typically include a plurality of very small, low-angle, openings within the walls of the pre-mix tubes that enable fuel to be injected from the nozzle head into the interior of the tubes, wherein the fuel and air can mix before exiting the tubes and entering a combustion chamber. Fuel injectors having a longer length facilitate enhanced mixing and therefore, enable increased operating efficiency and decreased emissions. However, the length of the fuel injector is generally limited by the thickness of the pre-mix tube, and tube thickness is generally limited by industry manufacturing standards and a desire to include as many tubes as possible within the fuel nozzle.
It should be appreciated that the above-descried fuel injection nozzles include many braze joints at the tube/plate and plate/wall interfaces that are required to seal the fuel. As a result, expensive EDM procedures are necessary to form the many small, low-angle fuel injection holes. In addition, intricate assembly methods are often required to meet specified performance criteria. As such, a need exists for a pre-mix tube that uses a longer fuel injector and that is manufactured with fuel nozzle geometries that reduce potentially leaky joints, and that reduces a need for post machining and/or EDM operations.